This invention relates in general to a pulse generator and more particularly to a pulse generator mechanism for generating a pulse in response to a switch in state of the magnetic wire disclosed in the above referenced patent application.
The magnetic device described in the above patent application is a ferro-magnetic wire having core and shell portions with divergent magnetic properties. These wires have come to be known in the art as Wiegand wires. One type of Wiegand wire is disclosed in U.S. Pat. No. 3,820,090. Another type of Wiegand wire is disclosed in the above referenced application.
The type of Wiegand wire of concern to the instant invention is one such that when the wire is subjected to a substantial magnetic field that is parallel to the axis of the wire, the entire wire will be magnetized in a first direction. As the external field is reduced in magnitude down to a zero field, the magnetization of the wire is unchanged. However, when the field reverses in direction, a small reverse field will cooperate with the shell to cause magnetization of the core to be reversed so that the flux generated by the shell will have its path completed through the relatively low reluctance core. The reversal in direction of the magnetization of the core can be sensed by a pickup coil to provide an output pulse.
When the direction of core magnetization and shell magnetization are opposite, the wire can be deemed to be in a reverse state. When core and shell magnetization are in the same direction, the state of the wire can be termed a confluent state.
As described in the referenced application, a preferred mode of switching this particular type of Wiegand wire is to first subject it to a sufficiently strong magnetization in a first or "positive" direction to force both core and shell into a confluent positive magnetization. The external field is then reduced in magnitude to zero and then beyond zero in a second or "negative" direction sufficiently to cause the core to change its direction of magnetization and thereby switch the state of the wire from confluent state to reverse state. After the reverse state has been achieved, then it is important that the magnitude of the external field in the second (i.e., negative) direction be limited and that the external field be reversed in direction again so as to go positive. The external field goes in a positive direction to a zero magnitude and then when the field becomes slightly positive, the state of the wire switches from its reverse state back to its confluent state. When the core changes its direction of magnetization during this switch of the wire from reverse state to confluent state, the change in the magnetization of the core is extremely rapid and the sensing core will provide a substantial output pulse in the order of a number of volts.
It is important that the external field have an asymmetric configuration in order to provide the maximum pulse when the wire switches from its reverse state to its confluent state. That is, it is important that the external field go strongly positive but not strongly negative. The external field must go negative enough to switch the state of the wire from its confluent state to its reverse state but not so strongly negative as to switch the shell.
Accordingly, an important purpose of this invention is to provide a pulse generating mechanism in which an external field is configured in a fashion that will provide the required asymmetric excitation so that the desired switching sequence is achieved. The desired switching sequence is determined by the fact that the greatest rate of change in flux occurs when the wire switches from its reverse state to its confluent state.
Accordingly, it is a purpose of this invention to provide a pulse generating mechanism that will operate on the particular type of Wiegand effect exhibiting wire described in the referenced patent application, to provide an appropriately configured field so as to provide a maximum output pulse in response to a switch in state of the wire.
It is a further purpose of this invention to provide this pulse generator in a package that is simple to use, relatively inexpensive and that will operate in a repeated and consistent fashion.
It is a related purpose of this invention to provide such a pulse generator device as will be useful in a wide variety of applications so that the pulse generator will be versatile.